This invention relates to an accumulator type fuel injection system.
There is an accumulator type fuel injection system (common rail system) as a fuel injection system for a diesel engine, capable of improving the engine performance in a wide operational region from a low-speed region to a high-speed region by stably supplying a high-pressure fuel accumulated in an accumulator to each cylinder of the engine. When a fuel injection rate immediately after the starting of a fuel injection operation is excessively high even in a case where such a fuel injection system is used, sudden explosion combustion is carried out in an initial stage of the combustion of the fuel, so that not only the engine noise but also the nitrogen oxide (NOx) content of an exhaust gas increases.
To eliminate such inconveniences, an accumulator type fuel injection system has been proposed which is adapted to inject a fuel at a lower fuel injection rate in an initial stage of each fuel injection cycle. The fuel injection system relating to this proposition is provided with, for example, a low-pressure accumulator adapted to store therein a low-pressure fuel, a high-pressure accumulator adapted to accumulate therein a high-pressure fuel, a change-over valve adapted to switch a fuel injection rate from one to another by communicating the low-pressure accumulator or the high-pressure accumulator selectively with an injector (fuel injection nozzle), and a switch valve adapted to control the fuel injection time by communicating and shutting off a pressure control chamber of the injector and a fuel tank with and from each other.
Regarding the formation of a fuel pressure in the accumulators, there is, for example, a fuel injection system adapted to obtain low-pressure and high-pressure fuels by using low-pressure and high-pressure fuel pumps which are driven by an engine respectively, or a fuel injection system adapted to obtain a high-pressure fuel by a high-pressure fuel pump, and a low-pressure fuel by regulating the pressure of the high-pressure fuel introduced into a low-pressure accumulator (for example, Japanese Patent Laid-Open 93936/1994).
In an accumulator type fuel injection system (for example, WO98/09068) adapted to obtain a low-pressure fuel in a low-pressure accumulator from a high-pressure fuel in a high-pressure accumulator, a fuel chamber (fuel reservoir) of an injector is filled with a low-pressure fuel with the injector kept closed by closing a fuel injection time control switch valve provided correspondingly to the injector in each cylinder, and switching a fuel injection rate change-over valve to a low-pressure side, and the injector is kept closed. When the fuel injection starting time comes, a switch valve is opened to open the injector and thereby carry out initial low-pressure injection (which will hereinafter be referred to as xe2x80x9clow-pressure injectionxe2x80x9d) of a fuel from a nozzle. When a low-pressure injection period elapses, the change-over valve is switched to a high-pressure side, and main high-pressure injection (which will hereinafter be referred to as xe2x80x9chigh-pressure injectionxe2x80x9d) is carried out by injecting the high-pressure fuel, which is supplied from the high-pressure accumulator, from the nozzle. When the injection finishing time comes, the change-over valve is switched to the low-pressure side with the switch valve closed at the same time. Namely, the controlling of an injection waveform of the fuel is done by switching the low-pressure and high-pressure accumulators from one to the other by the change-over valve during a fuel injection operation.
In the low-pressure accumulator, a low-pressure fuel is obtained by regulating the pressure of the high-pressure fuel collected between the change-over valve and the fuel chamber of the injector after the change-over valve is closed. Namely, the fuel in the low-pressure accumulator is discharged to a fuel tank (atmosphere-opened side) by controlling a duty of a pressure control valve, which is connected to the portion of a fuel passage which is between the low-pressure accumulator and fuel tank, of the low-pressure accumulator so that the fuel pressure in the low-pressure accumulator attains a predetermined level.
A case where the change-over valve provided correspondingly to the injector in each cylinder and adapted to switch a fuel injection rate gets out of order in the accumulator type fuel injection system of the above-described construction adapted to control an injection waveform by switching the low-pressure and high-pressure accumulators from one to the other will be discussed. When the change-over valve in one cylinder out of, for example, six cylinders or four cylinders gets out of order, the fuel injection pressure and fuel injection rate in the mentioned cylinder become abnormal in comparison with those in the remaining cylinders, and a decrease in the engine output and an increase in the fluctuation of torque occur in consequence, so that the engine cannot be normally operated. When the operation of the engine continues to be carried out in such an abnormal condition, damage to the engine or the vehicle occurs in some cases due to an overload, an increase in the exhaust gas temperature and the like.
When the pressure control valve provided in the low-pressure accumulator gets out of order after the valve is closed, the fuel pressure in the low-pressure accumulator increases, and finally becomes equal to that in the high-pressure accumulator. Consequently, high-pressure injection is carried out from an initial injection period, and the fuel injection rate becomes high to cause the engine to be subjected to an overload operation. Therefore, when the engine continues to be operated in such an abnormal condition, the engine or the vehicle is damaged in some cases. Since a permissible pressure resistance (permissible pressure) of the low-pressure accumulator is set lower than that of the high-pressure accumulator, an excessive increase in the fuel pressure in the low-pressure accumulator has a possibility of occurrence of damage to the low-pressure accumulator and leakage of fuel.
When the pressure control valve gets out of order while it is opened, the execution of low-pressure injection becomes impossible, and the high-pressure injection (main injection) only is carried out. This causes a delay of ignition time, an increase in the exhaust gas temperature and shortage of torque, and exerts ill influence upon the engine. Moreover, due to a necessary operation for increasing the pressure in the low-pressure accumulator, a high-pressure fuel supply pump carries out excessive force feeding of fuel repeatedly, so that there is the possibility that the high-pressure fuel supply pump gets out of order.
When a pressure sensor for detecting the fuel pressure in the high-pressure accumulator gets out of order (for example, the breaking of wire occurs) with a signal output at a low level in the accumulator type fuel injection system of the above-described construction adapted to control an injection waveform by switching the low-pressure and high-pressure accumulators from one to the other during a fuel injection operation, the fuel pressure in the high-pressure accumulator increases due to a necessary operation for controlling the same fuel pressure so that it increases. However, a relief valve provided in the high-pressure accumulator is finally operated, and damage to the high-pressure accumulator and fuel passage can be prevented.
However, the injecting of the fuel is necessarily done at an injection pressure not lower than a maximum level in a regular mode at all times, so that an increase in the injection rate, maximum inside-cylinder pressure and noise vibration occur. Moreover, due to a necessary operation for increasing the fuel pressure in the low-pressure accumulator, the high-pressure fuel pump repeats excessive force feeding of the fuel to give rise to a possibility of the occurrence of an accident.
When the pressure sensor of the high-pressure accumulator gets out of order with a signal output at a high level (high pressure), the fuel pressure in the high-pressure accumulator is necessarily controlled so that it decreases, so that the force feeding of the fuel from the same accumulator stops. Consequently, such a fuel pressure in the high-pressure accumulator that is required to carry out a fuel injection operation cannot be obtained. This makes it impossible to operate the engine.
When a pressure sensor for detecting the fuel pressure in the low-pressure accumulator gets out of order (for example, the breaking of wire occurs) with a signal output at a low level (low pressure), the fuel pressure in the low-pressure accumulator is necessarily controlled so that it increases, so that the fuel pressure in the same accumulator increases, and finally becomes equal to that in the high-pressure accumulator. Consequently, a high-pressure injection operation is carried out from an initial injection period, and the injection rate increases to cause the engine to be subjected to an overload operation. Therefore, when the engine continues to be operated in such an abnormal condition, the engine or the vehicle is damaged in some cases. Since the permissible pressure resistance (permissible pressure) of the low-pressure accumulator is set low with respect to that in the high-pressure accumulator, an excessive increase in the fuel pressure in the low-pressure accumulator gives rise to a possibility of the occurrence of damage to the low-pressure accumulator and the leakage of the fuel.
When the pressure sensor in the low-pressure accumulator gets out of order with a signal output at a high level (high pressure), the fuel pressure in the low-pressure accumulator is necessarily controlled so that it decreases, so that the pressure in the same accumulator reaches so low a level that a low-pressure injection operation cannot be carried out, a high-pressure injection operation only being thereby carried out. This causes a delay of the ignition time, an increase in the exhaust gas temperature and the shortage of torque, and exerts ill influence upon the engine.
Therefore, the present invention aims at providing an accumulator type fuel injection system adapted to prevent an engine trouble by judging a change-over valve provided correspondingly to a fuel nozzle in each cylinder and adapted to switch a fuel injection rate, a pressure control valve adapted to control a pressure in a low-pressure accumulator, and a fuel pressure detecting means for detecting a fuel pressure in the accumulators as to whether these valves and means break down or not; and carrying out, when they break down, a limp-home mode control operation in which an operational region of the engine is limited.
To achieve this object, the accumulator type fuel injection system according to the present invention has an accumulator adapted to store therein a fuel pressurized by a fuel pump, and a fuel injection valve to which the fuel stored in the accumulator is supplied, the fuel stored in the accumulator being injected from the fuel injection valve into a combustion chamber, the fuel injection system comprising a first accumulator adapted to store therein a high-pressure fuel pressurized by said fuel pump, a plurality of fuel injection valves connected to the first accumulator via a plurality of fuel passages and having nozzles for injecting the fuel into the combustion chambers of the engine, a plurality of first control valves provided in the fuel passages and adapted to control the discharging of the high-pressure fuel in the first accumulator to a downstream side of the fuel passages, a second accumulator adapted to store therein a fuel the pressure of which is lower than that of the high-pressure fuel in the first accumulator and connected via branch passages to the portions of the fuel passages which are on the downstream side of the first control valves, a second control valve adapted to control the discharging of the low-pressure fuel in the second accumulator to an atmosphere-opened side, a failure detecting means for detecting the occurrence of failure in the accumulator type fuel injection system, and a fuel control means adapted to control, during a regular operation of the engine, an operation for opening the first control valves in the midst of a period of time in which the fuel injection nozzles are opened and an operation for closing the first control valves simultaneously with the closure of the fuel injection nozzles, and set, when the occurrence of failure in the accumulator type fuel injection system is detected by the failure detecting means, a pressure of the fuel discharged from the fuel pump so that a fuel pressure in the fuel passages becomes not higher than a permissible pressure in the second accumulator.
When failure occurs in the accumulator type fuel injection system, the pressure in the fuel passages is maintained at a level not higher than that of a permissible pressure in the second accumulator at all times owing to this arrangement, so that the occurrence of engine trouble and damage to a vehicle can be prevented.
When the failure detecting means is formed so that it judges that at least one of the first control valves has got out of order, the exertion of a pressure of not lower than a permissible level on the second accumulator which occurs due to the execution of the high-pressure injection only of a fuel into, for example, the relative cylinder during a breakdown of the first control valve can be prevented.
When the failure detecting means is formed so that it judges that the second control valves have got out of order in a closed state, the occurrence of an uncontrollably high pressure in the second accumulator during a breakdown of the second control valves can be prevented.
When the fuel control means is formed so that it judges when a rate of opening of the second control valve with respect to a set pressure in the second accumulator is out of a reference region that the failure detecting means has got out of order when the controlling of the opening of the first control valves is done so as to discharge the high-pressure fuel in the first accumulator toward the second accumulator and when the controlling of the opening of the second control valve is done in accordance with an output from a fuel pressure detecting means, which is further provided for detecting the fuel pressure in the second accumulator, in such a manner that the fuel pressure in the second accumulator attains the set level, it becomes possible to judge the abnormality of the fuel pressure in the portions of the fuel passages which are between the first control valves and fuel injection nozzles, and prevent the occurrence of a breakdown of the engine and damage to a vehicle.
When the failure detecting means is formed so that it judges the occurrence of a breakdown of a first fuel pressure detecting means further provided for detecting the fuel pressure in the first accumulator, and, when the fuel control means is formed so that it controls by closing the second control valve when the breakdown of the first fuel pressure detecting means is detected by the failure detecting means the pressure of the fuel discharged from the fuel pump in accordance with an output from a second fuel pressure detecting means, which is further provided for detecting the fuel pressure in the second accumulator, in such a manner that the fuel pressure in the fuel passages reaches a level not higher than that of the permissible pressure of the second accumulator, the second accumulator is not damaged even when the first fuel detecting means gets out of order.
In addition, when the failure detecting means is formed so that it judges that the first fuel pressure detecting means gets out of order when a ratio of an average value of an absolute value of a variation rate with the lapse of time of an output from the first fuel pressure detecting means to an average value of an output therefrom is not higher than a predetermined level with a difference between the value of an output from the first fuel detecting means and a set pressure in the first accumulator not lower than a predetermined level, a failure judging accuracy can be improved.